To assist an automobile driver in managing increasing complexity and demands in road traffic, modern motor vehicles have a variety of different driver assistance systems. In principle, vehicle-related or road-traffic-related data are detected in these systems, analyzed, and used to control corresponding vehicle systems. Detection of the relevant data takes place via sensors. Using driver assistance systems such as anti-slip regulation (ASR), for example, spinning of wheels during startup of a vehicle is prevented, and locking of the wheels during braking is prevented with an antilock braking system (ABS). Sensors are widely used for this purpose for exact detection of a speed of the wheels of the motor vehicle.
A measurement of the speed of a wheel is performed in a contactless manner by detecting magnetic field fluctuations, which are caused by a rotation of a detection object or sensor rotor, for example an increment wheel, a ferromagnetic gearwheel, or a pole wheel, which rotates jointly with the respective wheel. The actual wheel speed sensor for detection of the magnetic field position is arranged so as to be stationary at a small distance from the sensor rotor.
Wheel speed sensors are differentiated on the basis of a mode of operation thereof into active and passive sensors. Inductive, passive sensors do not require a separate power supply. An inductive sensor has a coil and a permanent magnet, a magnetic effect of which extends up to an increment wheel. Rotational movement of the increment wheel and alternation of tooth and tooth gap linked thereto causes a change of the magnetic field. This change induces a measurable AC voltage. A frequency and amplitude of this AC voltage are proportional to a wheel speed.
In contrast to the passive wheel speed sensor, the active wheel speed sensor is supplied with a defined voltage. The active sensor supplies a signal having speed-independent constant amplitude and uses the Hall effect in detection of the speed signal. Ferromagnetic gearwheels, stamped plates or wheels having applied multi-poles, for example, are used as the detection object or sensor rotor.
Wheel speed sensors are typically arranged closely adjacent to the wheel, a velocity of which is to be measured, and to a corresponding transmission. There is an increased risk of corrosion in this environment. An array of protective casings and/or guide sleeves for the sensor head and/or the transition between sensor head and wiring harness of a wheel speed sensor are already known from the prior art.
An electromagnetic wheel speed sensor having a sensor head, a gearwheel and a cable is known, for example, from CN 205898835 U. The sensor head has a permanent magnet, a pole axis, and an inductive coil for measuring and generating an electromagnetic field. An output cable is guided by means of a cable conduit to a connecting part of a fastening aid and connected to an automobile body via an articulated connecting part.
CN 205273363 U discloses a connecting arrangement made of a wheel speed sensor and a wiring harness. Connection between the wiring harness and the wheel speed sensor includes injection-molded parts, wherein a section of a sensor head is enclosed using a casing. The casing includes protective sections that enclose the connection between the wiring harness and the sensor head. The probability of cable fractures can be reduced by means of a connecting arrangement, whereby reliability of the wheel speed sensor increases.
A wheel speed sensor comprising a rotation detection element for detecting a magnetic field fluctuation, which is caused by the rotation of a rotor, which rotates together with wheels of a vehicle, and is used as a detection object, is also known from JP 2015 141 129 A. The detected rotation is converted into an electrical signal and relayed by means of conductor sections of a rotation detection element to output wires. The output wires are encased by a cover part and countersunk therein, to ensure water tightness. The cover part is integrally embodied with a fixation part, which is used for a vehicle-side fixation of the wheel speed sensor. A seal element and a tubular element are arranged on the side of the fixation part facing away from the sensor head.
A metallic protective casing for a resin cover of a wheel speed sensor is known from JP 2008 268 016 A. The metallic protective casing is used to avoid damage that can arise due to collisions, adhesion, or movements of solids on the resin cover of the wheel speed sensor. The protective casing is designed to enclose the resin cover of a signal-detecting section of the wheel speed sensor. In particular, in a region of a rotating sensor rotor, detachment of particles can occur, in particular iron powder, which can move because of rotation of the sensor rotor and collide with the signal-detecting section. The signal-detecting section is therefore enclosed by the metallic protective casing, which is in turn connected to a provided wheel speed sensor.
KR 2015 009 3008 A discloses a wheel speed sensor comprising a speed sensor unit, within which a cable is connected to a speed sensor of a vehicle. An upper and a lower housing, which have an inner receptacle groove for accommodating the speed sensor unit, are embodied separately from one another. The upper housing may be detachably connected to the lower housing. In this manner, the same protective housing can be used to accommodate the wheel speed sensor independently of the structural design of a signal wheel and a vehicle-side fixation structure.
The wheel speed sensor, which is produced from plastic, typically does not itself corrode, however. Above all, a receptacle section, to which the wheel speed sensor is typically connected, is often subjected to corrosion. In particular, in wheel speed sensors that require a guide (lateral measurement sensors), this risk is increased. The guide functions are subjected to increased corrosion during assembly and be scratched or damaged in another manner. In this way, a removal of the wheel speed sensor is often only performed with damage up to destruction of the sensor or is even completely impossible.
DE 10 2009 054 521 A1 discloses a fastening device to fasten a speed sensor housing of a wheel speed sensor on a vehicle. For this purpose, an adapter is provided, comprising a cylindrical main part, on one end of which a fastening flange protrudes laterally. The fastening flange has a borehole, so that the adapter can be fastened by means of a screw on the vehicle. The sensor housing is provided on its outer side with two flattened areas, which form a twist lock with corresponding inner faces of the cylindrical main part of the adapter, to secure the wheel speed sensor in an exact alignment in relation to the sensor wheel.
In consideration of the prior art shown, wheel speed sensors still offer room for improvements.